net_sched: sch_fq: prefetch one skb ahead in dequeue()

net_sched: sch_fq: prefetch one skb ahead in dequeue()

prefetch the skb that we are likely to dequeue at the next dequeue().

Also call fq_dequeue_skb() a bit sooner in fq_dequeue().

This reduces the window between read of q.qlen and
changes of fields in the cache line that could be dirtied
by another cpu trying to queue a packet.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20251121083256.674562-10-edumazet@google.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>